Fulltext Search Nextcloud with Elasticsearch

Hi All, I’m not sure if I’m right here but I have to start somewhere.
I’m running LSIO/nextcloud and I want to implement the full text search.

The ES-Container is running and I did also build with Dockerfiles the Image with the required Plugin. The Container is coming up and is exposed on Port 9200 correctly.

I configured in Nextcloud the Fülltest-Search App as documented.

Now to the actual problem:
When I want to index the thing, this error message is showing:

root@44d23653bbf3:/config/www/nextcloud# sudo -u abc php7 ./occ fulltextsearch:index
In Index.php line 381:
  failed platform test.
fulltextsearch:index [--output [OUTPUT]] [-r|--no-readline] [--] [<options>]

some one any idea how can I solve the problem?
Thanks a lot for the help and kind regards

PS: I can also provide all commands which I used to set up the Container.